Conventionally, inkjet recording apparatuses are broadly known as a type of liquid ejection apparatus. Inkjet recording apparatuses include “off-carriage” types in which an ink retainer is connected to a recording head through an ink supply tube. The ink retainer is provided in an ink cartridge as an ink container. The ink retainer is pressurized by pressurized air introduced into the ink cartridge by means of, for example, a pump. This causes the ink in the ink retainer to be sent to the recording head through the ink supply tube, so that the recording head is supplied with the ink. The ink is then ejected from the nozzles of the recording head to a recording paper as ink droplets for recording characters or images.
Typically, the inkjet recording apparatuses perform cleaning, or discharge bubbles or ink with increased viscosity from the nozzles of the recording head to a waste ink tank, when necessary for preventing ink ejection problems.
In the off-carriage type inkjet recording apparatuses, the waste ink tank may be formed integrally with the ink cartridge. A variety of such apparatuses have been proposed (see, for example, Patent Document No. 1).
As shown in FIG. 7, Patent Document No. 1 describes an inkjet recording apparatus 100 having an ink tank 102 for accommodating an ink pack 101. The ink pack 101 is connected to a recording head 105 through an ink supply tube 104 connected to an ink supply port 103 of the ink tank 102. The inkjet recording apparatus 100 further includes a cap 106 for receiving waste ink from the recording head 105. The cap 106 is connected to a pressurization port 109 of the ink tank 102 through an ink recovery tube 107 and a pump 108. A valve 112 and a pressure sensor 113 are connected to a discharge port 110 of the ink tank 102 through a passage 111. The valve 112 opens the ink tank 102 when necessary. The pressure sensor 113 detects the pressure in the ink tank 102. A stopper 114 is formed in the ink supply tube 104 for selectively prohibiting and permitting a flow of ink in the ink supply tube 104.
When the pump 108 is activated with the ink supply tube 104 held open by the stopper 114, the waste ink and the air are introduced from the cap 106 into the ink tank 102 through the ink recovery tube 107. This raises the pressure in the ink tank 102 and thus squeezes the ink pack 101, supplying the ink to the recording head 105 through the ink supply tube 104.
When the inkjet recording apparatus 100 operates to restore ink ejection performance, the stopper 114 blocks the ink supply tube 104 and the pump 108 is activated. When the pressure in the ink tank 102 reaches a predetermined level, the ink supply tube 114 is opened. This causes the ink to flow to the recording head 105 rapidly, thus removing the ink and the bubbles in the ink from a nozzle portion of the recording head 105. In this manner, the ink ejection performance is restored through pressurization.
In the inkjet recording apparatus 100, it is desired that the ink be supplied to the recording head 105 appropriately for performing printing effectively. It is thus necessary to maintain the ink pack 101 in an appropriately pressurized state.
Liquid ejection apparatuses are now required to be compact and gear pumps, which satisfy such requirement, are capturing attention.
However, if the inkjet recording apparatus 100 includes a gear pump and suction maintenance performance of the pump is lowered due to a manufacturing error in the pump, the air or the ink may flow back to the cap 106. This makes it difficult to maintain the ink pack 101 in an appropriately pressurized state. If backflow of the ink occurs, a mixture of the waste ink and the air leaks to the cap 106, generates bubbles in the cap 106, and thus contaminates the recording head 105.
Further, when the inkjet recording apparatus 100 seals the nozzles of the recording head 105 by means of the cap 106, the inkjet recording apparatus 100 forms a closed circulatory system. Therefore, if the pressure in the cap 106 and the pressure in the recording head 105 are not equilibrated, or the pressure in the cap 106 becomes higher than the pressure in the recording head 105, the air and the waste ink may flow back from the cap 106 to the recording head 105.
If the suction maintenance performance of the gear pump is relatively low, the air and the waste ink flow to the ink tank 102 when the gear pump is activated, with the nozzles of the recording head 105 sealed by the cap 106. However, if the gear pump stops, the air and the waste ink may flow back to the cap 106. Such air and waste ink may enter the recording head 105 through the nozzles of the recording head 105. This influences meniscus of the ink produced in the nozzles to a certain extent, thus hampering desirable ink ejection of the inkjet recording apparatus 100.
Patent Document No. 1: Japanese Laid-Open Patent Publication No. 2001-162838